eCPM, RPM, ARPDAU and fill rate in plain English
Four numbers decide what your ads earn. What each one measures, how to work it out yourself, and which one to watch.
Every ad dashboard opens with a wall of acronyms. You can ignore most of them. These four are the ones worth understanding, and they fit together into a single formula.
eCPM
Effective cost per mille, where mille means a thousand. It's what you earned for every 1,000 ads shown, regardless of whether the advertiser was paying for views, clicks or installs. Google's AdMob reports glossary defines it as estimated earnings divided by impressions, times 1,000.
If 200,000 impressions earned $600, that's $600 ÷ 200,000 × 1,000 = $3.00.
It's the standard way to compare formats, networks and countries. On its own it says nothing about how much you earned, because it leaves out volume.
RPM
Revenue per mille. Website publishers use it, usually per 1,000 pageviews rather than per 1,000 impressions. A page can carry several ads, so page RPM is often higher than the eCPM of any one ad on it.
50,000 pageviews that earned $400 is a page RPM of $8.00. Some networks report session RPM (per 1,000 visits) instead. When you compare networks, make sure you're comparing the same kind of RPM.
Fill rate
Your app asks for an ad and sometimes nothing comes back. Fill rate is the share of requests that did return one. AdMob calls it match rate.
Fill tends to be lower in smaller markets and for less common formats. Mediation helps, because when one network has nothing, another may.
ARPDAU
Average revenue per daily active user: a day's ad earnings divided by the number of people who used the app that day.
$150 from 25,000 daily users is an ARPDAU of $0.006. That looks tiny, but multiply it by the number of users and days and it adds up.
This is the one to watch. It already includes eCPM, fill, how many ads each person sees and which formats you run. If a change pushes eCPM up and ARPDAU down, the change made you less money.
How they fit together
That's the whole model, and it's what the calculator on our home page runs, using benchmark eCPMs per format, network and region. It's also a useful way to diagnose a problem. If eCPM looks normal and revenue is still low, look at fill or ads per user. If impressions are high and revenue isn't, the price is the problem: audience, format or network.